Heating apparatus for scan lamp

ABSTRACT

An illuminating apparatus in which the temperature thereof is regulated for producing light rays having a substantially constant spectral energy distribution.

United States Patent 1191 Kidd Dec. 18, 1973 HEATING APPARATUS FOR SCANLAMP 2,581,959 1/1952 Koehler 313/15 x 3,482,9l8 ill/I969 Nederlof....240/47 X [75] Inventor: Wayne L. Kidd, Fa1rport, N.Y. 3.14162] 7/1964Tolbenm 0/47 X [73] Assigneez Xerox corporatiomstanword Com 3,112,89012/1963 Snelling 240/47 x [22] Filed: Oct. 13, 1972 PrimaryExaminer-Richard L. Moses [2]] Appl' 297,520 Attorney-James J. Ralabateet al.

[52] US. Cl 355/8, 240/47, 313/15, 355/4, 355/67 [51] Int. Cl. G03g15/00, G03b l5/02 [57] ABSTRACT [58] Field of Search 240/47; 355/4, 67,

355/70, 313/ 2, 15 An illuminating apparatus in which the temperaturethereof is regulated for producing light rays having a [56] ReferencesCited substantially constant spectral energy distribution.

UNITED STATES PATENTS 3,330,l80 7/1967 Ferguson et a]. 240/47 X 14Claims, 3 Drawing Figures PATENTEUUEE 18 1915 3.779 640 sum 1 or 2HEATING APPARATUS FOR SCAN LAMP BACKGROUND OF THE INVENTION Thisinvention relates generally to an electrophotographic printing machine,and more particularly concerns an illuminating apparatus having thespectral en ergy distribution of the light rays being disseminatedtherefrom substantially constant.

In the process of electrophotographic printing, a photoconductivesurface is uniformly charged and exposed to a light image of an originaldocument. Exposure of the photoconductive surface records thereon anelectrostatic latent image corresponding to the original document. Theelectrostatic latent image is then rendered visible by depositingthereon toner particles which adhere electrostatically thereto in imageconfiguration. Subsequently, the toner powder image is transferred to asheet of support material which may be plain paper or a transparentthermoplastic material, amongst others. The toner powder image is, then,permanently affixed to the support material, thereby providing a copy ofthe original document.

Multi-color electrophotographic printing is substantially the same asthe heretofore discussed process with the following distinctions. Ratherthan forming a total light image of the original, the light image isfiltered producing a single color light image which is a partial lightimage of the original. The foregoing single color light image exposesthe charged photoconductive surface recording thereon a single colorelectrostatic latent image. This single color latent image is developedwith toner particles of a color complementary to the single color lightimage. Thereafter, the single color toner powder image is transferred tothe support material. The foregoing process is repeated a plurality ofcycles with difi'erently colored light images and the respectivecomplementary colored toner particles. Each single colored toner powderimage is transferred to the support material in superimposedregistration with the prior toner powder image to form a compositemultipowder image thereon. This multi-color powder image is coalescedand permanently affixed to the support material.

It is, apparent that in a multi-color electrophotographic printingmachine, the spectral characteristics of the illuminating apparatus arecritical. Preferably, the spectral energy distribution of the lightsource in the illuminating apparatus remains substantially constant.Thisis desirable to insure that the filtered light image has thespecified bandwidth and amplitude. In turn, the photoconductive memberis designed to be responsive to the bandwidth and amplitude of the lightimage being transmitted through the filter. Variations in bandwidthand/or amplitude will create variations in the color balance of thereproduction.

A typical light source may be a tri-phosphor fluorescent lamp. This typeof lamp is arranged to have peak energy outputs at the blue, green andred wavelengths. The corresponding filters are arranged to permit asingle color light image topass therethrough. Hence, a blue filter onlypermits the blue light image to be transmitted therethrough, a redfilter only a red light image and a green filter only a green lightimage. It is apparent that if the spectral energy distribution of thelamp should vary, the amplitude and/or bandwidth of the filtered lightimage may be changed. For example, if the spectral energy distributionof the lamp varies such that the blue light image is of a too narrow abandwidth and- /or of a low amplitude, a weak blue light image will beformed. This weak blue image will, in turn, record a weak electrostaticlatent image on the photoconductive member, and the complementary tonerpowder image will be course be weak. However, the toner powder imagescomplementary to the red and green filtered light images will be ofnormal strength resulting in the copy having a distorted color balance.

Fluorescent lamps generally are sensitive to thermal variations in thesurrounding environment. Typical fluorescent lamps have a discreteamount of liquid mercury deposited within a phosphor coated lamp bulb.During lamp operation, the mercury is vaporized to a very low pressuregenerating a mercury line radiation at a wavelength of 253.7 nm. Thisradiation is absorbed by the phosphor coating producing radiation in thevisible spectrum. The spectral energy distribution of the lamp is afunction of the 253.7 nm mercury line radiation, which, in turn, is afunction of the mercury vapor pressure within the lamp bulb. However,the mercury vapor pressure is dependent upon the lamp bulb temperature.Thus, amplitude and/or the bandwidth of the respective spectral energyoutputs from the lamp are dependent upon temperature gradients.

In an electrophotographic printing machine, particularly a multi-colormachine, heat is continually being dissipated by the exposure mechanism,and the fusing apparatus adapted to coalesce and fix the powder image tothe support material. It is evident that thermal gradients of thisnature may adversely effect the spectral energy distribution of theilluminating apparatus.

Accordingly, it is a primary object of the present invention to improvethe temperaturecontrol system of an illuminating apparatus maintainingthe spectral energy distribution therefrom substantially constant.

SUMMARY OF THE INVENTION Briefly stated, and in accordance with thepresent invention, there is provided an illuminating apparatus in whichthe spectral energy distribution therefrom is maintained substantiallyconstant.

This is accomplished in the present instance by a light source havingheating means entrained about a portion of the exterior peripheralsurface thereof. In addition, cooling means, spaced from the lightsource, are provided. Regulating means control the cooling and heatingmeans to maintain the light source substantially at a predeterminedtemperature. In this manner, the spectral energy distribution of thelight rays emitted from the light source are unaffected by thermaldisturbances and remains substantially constant.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of thepresent invention will become apparent upon reading the followingdetailed description and upon reference to the drawings, in which:

FIG. I is a schematic perspective view of an electrophotographicprinting machine having the present invention therein;

FIG. 2 is a schematic illustration of the illuminating apparatusincorporated in the FIG. 1 printing machine, and

FIG. 3 is a perspective view of the light source utilized in the FIG. 2illuminating apparatus.

While the present invention will be described in connection with apreferred embodiment, it will beunderstood that it is not intended tolimit the invention to that embodiment. On the contrary, it is intendedto cover all alternatives, modifications and equivalents as may beincluded within the spirit and scope of the invention as defined by theappended claims.

DETAILED DESCRIPTION OF INVENTION Whith continued reference to thedrawings wherein like reference numerals have been used throughout toindicate like elements, FIG. 1 schematically illustrates the componentsof an electrophotographic printing machine for producing multi-colorcopies from a colored original.

As shown schematically in FIG. 1, the electrophotographic printingmachine, particularly adapted to utilize the present invention, includesa rotatably mounted drum having a photoconductive surface 12 thereon.Drum 10 is mounted on a shaft journaled in the printing machine frame torotate in the direction indicated by arrow 14 causing photoconductivesurface 12 to pass sequentially through processing stations A through E,inclusive.

Initially, drum 10 rotates in the direction of arrow 14 to movephotoconductive surface 12 through charging station A. Charging stationA has positioned thereat a corona generating device indicated generallyat 16. As illustrated in FIG. 1, corona generating device 16 is arrangedto extend in a generally transverse direction across photoconductivesurface 12. Corona generating device 16 charges photoconductivesurface12 to a relatively high substantially uniform potential. US. Pat. No.2,778,946 issued to Mayo in 1957 describes a typical corona generatingdevice which may be suitable for use in a multi-colorelectrophotographic printing machine.

'After photoconductive surface 12 is charged to a substantially uniformpotential, drum 10 rotates to exposure station B. At exposure station B,photoconductive surface 12 is exposed to a single color light image ofthe original document. A moving lens system, gener ally designated bythe reference numeral 18, and a color filter mechanism, shown generallyat 20 are positioned at exposure station B. One type of moving lenssystem suitable for the electrostatographic printing machine of FIG. 1is disclosed in U.S. Pat. No. 3,062,108 issued to Mayo in 1962. Originaldocument 22 is supported stationarily upon transparent viewing platen24. The lamp assembly, indicated generally at 25, includes a pair oflamps 26, associated with lens system 18. Lamps 26 move in a timedrelation with drum 10 scanning successive incremental areas of originaldocument 22 positioned upon platen 24. This creates a flowing lightimage of original 22 which is recorded on photoconductive surface 12.During the exposure process, filter mechanism 20 interposes selectedcolored filters into the optical light path of lens 18. The color filteroperates on the light rays transmitted through lens 18 to record asingle color electrostatic latent image on photoconductive surface 12corresponding to a preselected spectral region of the electromagneticwave spectrum.

After the single color electrostatic latent image is recorded onphotoconductive surface 12, drum 10 rotates to development station C.Development station C includes three individual developer units,generally indicated by the reference numerals 28, 30 and 32, re-

spectively. A suitable development system utilizing a plurality ofdeveloper units is disclosed in copending application Ser. No. 255,259filed in 1972. As disclosed in the foregoing patent application, thedeveloper units are all magnetic brush development units. Typicalmagnetic brush developer units utilize a magnetizable developer mixincluding carrier granules and toner particles. This developer mix isbrought continually through a directional flux field to form a brushthereof. Development is achieved by bringing the single colorelectrostatic latent image recorded on photoconductive surface 12 intocontact with the brush of developer mix. Differently colored tonerparticles corresponding to the complement of the spectral region of thewavelength of light transmitted through filter 20 are contained withineach of the respective developer units. For example, a green filteredelectrostatic image is made visible by depositing green absorbingmagneta toner particles thereon. Similarly, blue and red latent imagesare developed with yellow and cyan toner particles respectively,

Subsequent to the formation of the toner powder image on photoconductivesurface 12, drum 10 is rotated to transfer station D. At transferstation D, the powder image adhering electrostatically tophotoconductive surface 12 is transferred to a sheet of final supportmaterial 34. Final support material 34 may be plain paper or, in theformation of transparencies, a thermoplastic transparent material. Abias transfer roll, shown generally at 36, recirculates support material34 in the direction of arrow 38. Roll 36 is electrically biased to apotential of sufficient magnitude and polarity to electrostaticallyattract toner particles from photoconductive surface 12 to sheet 34. US.Pat. No. 3,612,677 issued to Langdon in 1972 discloses a suitableelectrically biased transfer roll. Transfer roll 36 is arranged torotate in synchronism with photoconductive surface 12, i.e. transferroll 36 and drum l0 rotate substantially at the same speed and havesubstantially the same outer diameter. Inasmuch as support material 34is secured releasably to transfer roll 36 for movement therewith in arecirculating path, successive toner powder images may be transferredthereto. Hence, successively colored toner particles are transferredfrom photoconductive surface 12 to support material 34 in superimposedregistration with one another. In this way, a multi-colored toner powderimage corresponding to the colors found in the original document isformed on support material 34.

With continued reference to FIG. 1, the paper path for advancing supportmaterial 34 to transfer roll 36 will hereinafter be described. Stack 40of support material 34 is supported on tray 42. Feed roll 44 operativelyassociated with retard roll 46 separates and advances the uppermostsheet from stack 40. The advancing sheet moves into paper chute 48 andis directed into the nip of register rolls 50. Next, gripper fingers 42,mounted on transfer roll 36, releasably secure thereto support material34 for movement therewith in a recirculating path.

After all of the discretely colored powder images have been transferredto support material 34, support material 34 is stripped from transferroll 36 and moved on endless belt conveyor 54 to fixing station E, wherea fuser indicated generally at 56, coalesces and permanently affixes thetransferred powder image to sheet 34. A typical fuser is described inUS. Pat. No. 3,498,592

issued to Moser et al. in 1970. After the powder image is fused, supportmaterial 34 is advanced by endless belt conveyors 58 and 60 to catchtray 62. At catch tray 62, an operator may remove the final multi-colorcopy from the machine.

As indicated by arrow 14, the final process in the direction of rotationof drum is cleaning station F. Preferably, brush cleaning device 64positioned at cleaning station F, is of the type described in U.S. Pat.No. 3,590,412 issued to Gerbasi in 1971. As disclosed therein, arotatably mounted fibrous brush is maintained in contact withphotoconductive surface 12 to remove residual toner particles remainingthereon after each transfer operation.

The apparatus of the present invention is associated with maintainingthe spectral energy output of lamp 26 substantially constantand will bediscussed, hereinafter, in detail,. in association with FIGS. 2 and 3.As heretofore indicated, lamp 26, preferably, is of the typeconventionally referred to as a fluorescent lamp. Typical fluorescentlamps are sensitive to variations in the surrounding thermalenvironment. It is, therefore, evident that it would be desirable tomaintain the thermal environment surrounding lamp 26 substantiallyconstant.

Turning now to FIG. 2, there is shown lamp carriage 56 supporting a pairof light sources or lamps 26 therein. Lamp carriage 66 is arranged totraverse platen 24 illuminating incremental widths of original 22.Heating means or sleeve heater 68 is arranged to supply energy to lightsource 26. Sleeve heater 68 has an arcuate portion arranged to bemounted slidably on lamp 26 extending about the entire longitudinallength thereof, and in substantial contact with a portion of theexterior circumferential surface thereof. The arcuate portion extendsover a 270 arc with a slot extending the entire length of lamp 26permitting light rays to pass therethrough. Heater 68, preferably, has awatt output and operates at a voltage ranging from about 98 volts to 127volts at about 60 hertz. The wire resistance elements incorporated inheater 68 have a resistance of about 685 ohms. The laminated structuresurrounding the wire resistant elements is a polyester impregnated glasscloth laminated over a nomex substrate or, in lieu thereof, a nichromewire grid laminated in an insulation of teflon and epoxy coated glasscloth. The exterior surface of the heater is coated with a flat blackpaint arranged to withstand an operating temperature of about 175 F.Sleeve heater 68 engages the exterior surface of lamp 26 with a pull-outforce ranging from about 1 pound to about 5 pounds, and preferably isabout 3 pounds. Cooling means or blower 70 is secured to lamp carriage66. Blower 70 creates a flow of air, in the direction of arrow 72, uponlamp 26 for reducing the temperature thereof. In this way, heater 68 mayraise the temperature of lamp 26 when it is beneath a predeterminedtemperature, and blower 70 may reduce the temperature of lamp 26 when itexceeds a predetermined temperature. Blower 70 is a centrifugal blowerhaving a two-pole permanent split capacitormotor, and operates at about1 17 volts, 60 hertz with about a 53 CFM capacity at a sea level staticpressure of about 0 inches of water. Air filter 71 is secured to theintake of blower 70. The density of the air filter is critical inestablishing the flow characteristics of the system. Preferably, filter71 is made from a foam material having a density of 45 pores per linearinch. Regulating means,

operatively associated with heater 68 and blower 70 maintain lamp 26substantially at about the predetermined temperature, preferably, 100 F.The predetermined temperature may range from about F to about 115 F.

Referring now to FIG. 3, there is shown a single lamp 26 having a sleeveheater 68 wrapped thereabout. As shown in FIG. 3, sleeve heater 68extends the entire length of lamp 26 about 270 arc. The exteriorcircumferential surface of lamp 26 is opaque with a clear region 74extending over a 45 arc therein. Region 74 extends substantially theentire length of tubularly configured lamp 26. Lamp 26 operates at about30 watts, 37 volts and 1.5 amps RMS. The spectral energy distribution ofthe red output is about 44 micro watts per centimeter squared, the greenoutput about 82 micro watts per centimeter squared, and the blue outputabout 25 micro watts per centimeter squared. The lamp includes threephosphors having a color balance such that the blue/green ratio is 0.3and the red/green is about 0.53.

As depicted in FIG. 3, the regulating means includes suitable circuitmeans (not shown) and/or a thermally responsive member 76. Thermallyresponsive member 76 is, preferably, a hermatically sealed bi-metal snapaction disc type thermostat. The contacts of thermostat 76 are rated atabout 0.5 amps, 117 volts AC at 60 hertz. The contacts open at about 110F and close at about Ft Preferably, thermostat 76 is positioned on thewall of lamp 26 substantially at the center of the slot in sleeve heater68. Thermostat 76 is an on-off type of device. In operation, when lamp26 is heated to a temperature greater than F, the contacts of thermostat76 open de-energizing sleeve heater 68. Since blower is continuallyoperative, the How of air therefrom reduces the temperature of lamp 26.When the temperature of lamp 26 is beneath 100 F, the contacts ofthermostat 76 close energizing sleeve heater 68. In this way, lamp 26 ismaintained within a temperature ransissfmtabout IOOLEI about While theinvention has been described in connection with an on-off type ofthermostat, one skilled in the art will appreciate that the-invention isnot necessarily so limited and that a proportional thermistor isconjunction with suitable circuit means may be utilized to control thetemperature of lamp 26. For example, a proportional thermistor may beconnected as one leg of a conventional Wheatstone bridge circuit. Theresulting error signal is indicative of the deviation in lamptemperature from the predetermined temperature. This error signal may beutilized to de-energize sleeve heater 68 when the predeterminedtemperature is exceeded. Similarly, the error signal energizes sleeveheater 68 when the lamp temperature is beneath the predeterminedtemperature.

The foregoing types of control schemes maintain the temperaturesurrounding lamp 26 substantially constant. This insures that the lightrays emitted from lamp 26 have a substantially constant spectral energydistribution. Thus, the various electrostatic images recorded onphotoconductive surface 12 have the color content thereof properlybalanced with one another.

In recapitulation, it is evident that the thermal environmentsurrounding the light source utilized in the electrophotographicprinting machine heretofore described is maintained substantiallyconstant. Hence, thermal fluctuations in the surrounding environment areminimized and the spectral energy output thereform is maintainedsubstantially constant. This is achieved by sleeve heater 68, blower 70,and thermostat 76. In operation, a thermal control range is developed bythe interaction of heater 68, blower 70 and thermostat 76. When theupper temperature limit of this control range is approached, thermostat76 deenergizes heater 68. Cooling air from blower 70 reduces thetemperature of lamp 26 beneath the upper temperature limit. When thelower temperature limit of the control range is approached, thermostat76 energizes heater 68 transferring thermal energy to lamp 26. Theresulting interaction of cooling air from blower 70, self heating fromlamp 26, and thermal energy from lamp 26 maintain lamp 26 at atemperature equilibrium within the specified temperature control range.Therefore, the present invention improves the temperature control of theilluminating apparatus utilized in multicolor electrophotographicprinting machines, thereby maintaining the spectral energy distributiontherefrom substantially constant. This, in turn, insures that the colorbalance of the copy compares favorably with the original.

It is, therefore evident that there has been provided, in accordancewith the present invention, an illuminating apparatus that fullysatisfies the objects, aims and advantages set forth above. While thisinvention has been described in conjunction with specific embodimentsthereof, it is evident that many alternatives, modifications andvariations will be apparent to those skilled in the art. Accordingly, itis intended to embrace all alternatives, modifications and variationsthat fall within the spirit and broad scope of the appended claims.

I claim:

1. An illuminating apparatus, including:

a substantially elongated tubular tri-phosphor light source having asubstantially opaque region extending over a portion of the exteriorcircumferential surface thereof from about one end portion of said lightsource to about the other end portion thereof, and a substantiallytransparent region extending over the remaining portion of the exteriorcircumferential surface of said light source;

heating means entrained substantially about the opaque region of theexterior circumferential surface of said light source and arranged tosupply energy to said light source, said heating means being an arcuatemember arranged to mount slidably on said light source in substantialcontact with the opaque region of the exterior circumferential surfacethereof, said arcuate member extending in a longitudinal direction fromabout the region of one end portion of said light source to about theregion of the other end portion thereof and having a slot thereinextending in a longitudinal direction from one end portion of said lightsource to the other end portion thereof permitting light raystransmitted through the transparent region of said light source to passtherethrough;

means for cooling said light source, said cooling means being spacedfromsaid light source; and

means for regulating said cooling means and said heating means tomaintain said light source substantially at about a predeterminedtemperature.

2. An illuminating apparatus as recited in claim 1, wherein said arcuatemember extends circumferentially preferably, about 270.

3. An illuminating apparatus as recited in claim 1, wherein said coolingmeans. includes blower means adapted to create a flow of air upon saidlight source.

4. An illuminating apparatus as recited in claim 1, wherein saidregulating means includes:

a thermally responsive member contacting the exterior peripheral surfaceof said light source for detecting the temperature thereof; and

circuit means operatively associated with said thermally responsivemember for energizing said heating means when said thermally responsivemember indicates that the temperature of said light source is beneath apredetermined value, said circuit means being adapted to de-energizesaid heating means when said thermally responsive member indicates thatthe temperature of said light source exceeds the predetermined value.

5. An illuminating apparatus as recited in claim 4, wherein thepredetermined value of the temperature of said light source ranges fromabout F to about 1 15 F, and preferably is about F.

6. An illuminating apparatus, as recited in claim 1, wherein saidregulating means includes a thermally responsive member contacting theexterior peripheral surface of said light source for detecting thetemperature thereof, said thermally responsive member energizing saidheating means when the temperature of said light source is beneath apredetermined lower value and de-energizing said heating means when thetemperature of said light source is above a predetermined upper value.

7. An illuminating apparatus as recited in claim 6, wherein the lowervalue of the temperature of said light source preferably is about 100 Fand the upper value of the temperature of said light source preferablyis about 1 10 F.

8. A multi-color electrophotographic printing machine of the type havingan apparatus for illuminating longitudinal sections of incremental widthof an original document during the scanning thereof, and means forexposing a photoconductive surface to the light image thereof, whereinthe improvement includes:

a substantially elongated tri-phosphor light source having asubstantially opaque region extending over a portion of the exteriorcircumferential surface thereof from about one end portion of said lightsource to about the other end portion thereof, and a substantiallytransparent region extending over the remaining portion of the exteriorcircumferential surface of said light source;

heating means entrained substantially about the opaque region of theexterior circumferential surface of the light source and arranged tosupply energy to the ligh source, said heating means being an arcuatemember arranged to mount slidably on said light source in substantialcontact with the opaque region of the exterior circumferential surfacethereof, said arcuate member extending in a longitudinal direction fromabout the region of one end portion of said light source to about theregion of the other end portion thereof and having a slot thereinextending in a longitudinal direction from one end portion of said lightsource to the other end portion thereof permitting light raystransmitted through the transparent region of said light source to passtherethrough;

said cooling means includes blower means adapted to create a flow of airupon the light source.

means for cooling the light source, said cooling means being spaced fromthe light source; and

means for regulating said cooling means and said heating means tomaintain the light source substantially at about a predeterminedtemperature.

9. A printing machine as recited as claim 8, wherein said arcuate memberextends circumferentially preferably, about 270.

10. A printing machine as recited in claim 8, wherein 11. A printingmachine as recited in claim 8, wherein said regulating means includes:

when said thermally responsive member indicates that the temperature ofthe light source exceeds the predetermined value.

12. A printing machine as recited in claim 11, wherein the predeterminedvalue of the temperature of the light source ranges from about F toabout 1 15 F, and preferably is about F.

13. A printing machine as recited in claim 8, wherein said regulatingmeans includes a thermally responsive member contacting the exteriorperipheral surface of the light source for detecting the temperaturethereof, said thermally responsive member energizing said heating meanSwhen the temperature of the light source is beneath a predeterminedlower value of de-energizing said heating means when the temperature ofthe light source is above a predetermined upper valve.

14. A printing machine as recited in claim 13, wherein the lower valueof the temperature of the light source preferably is about 100 F and theupper valve of the temperature of the light source preferably is about 110 F.

1. An illuminating apparatus, including: a substantially elongatedtubular tri-phosphor light source having a substantially opaque regionextending over a portion of the exterior circumferential surface thereoffrom about one end portion of said light source to about the other endportion thereof, and a substantially transparent region extending overthe remaining portion of the exterior circumferential surface of saidlight source; heating means entrainEd substantially about the opaqueregion of the exterior circumferential surface of said light source andarranged to supply energy to said light source, said heating means beingan arcuate member arranged to mount slidably on said light source insubstantial contact with the opaque region of the exteriorcircumferential surface thereof, said arcuate member extending in alongitudinal direction from about the region of one end portion of saidlight source to about the region of the other end portion thereof andhaving a slot therein extending in a longitudinal direction from one endportion of said light source to the other end portion thereof permittinglight rays transmitted through the transparent region of said lightsource to pass therethrough; means for cooling said light source, saidcooling means being spaced from said light source; and means forregulating said cooling means and said heating means to maintain saidlight source substantially at about a predetermined temperature.
 2. Anilluminating apparatus as recited in claim 1, wherein said arcuatemember extends circumferentially preferably, about 270*.
 3. Anilluminating apparatus as recited in claim 1, wherein said cooling meansincludes blower means adapted to create a flow of air upon said lightsource.
 4. An illuminating apparatus as recited in claim 1, wherein saidregulating means includes: a thermally responsive member contacting theexterior peripheral surface of said light source for detecting thetemperature thereof; and circuit means operatively associated with saidthermally responsive member for energizing said heating means when saidthermally responsive member indicates that the temperature of said lightsource is beneath a predetermined value, said circuit means beingadapted to de-energize said heating means when said thermally responsivemember indicates that the temperature of said light source exceeds thepredetermined value.
 5. An illuminating apparatus as recited in claim 4,wherein the predetermined value of the temperature of said light sourceranges from about 90* F to about 115* F, and preferably is about 100* F.6. An illuminating apparatus, as recited in claim 1, wherein saidregulating means includes a thermally responsive member contacting theexterior peripheral surface of said light source for detecting thetemperature thereof, said thermally responsive member energizing saidheating means when the temperature of said light source is beneath apredetermined lower value and de-energizing said heating means when thetemperature of said light source is above a predetermined upper value.7. An illuminating apparatus as recited in claim 6, wherein the lowervalue of the temperature of said light source preferably is about 100* Fand the upper value of the temperature of said light source preferablyis about 110* F.
 8. A multi-color electrophotographic printing machineof the type having an apparatus for illuminating longitudinal sectionsof incremental width of an original document during the scanningthereof, and means for exposing a photoconductive surface to the lightimage thereof, wherein the improvement includes: a substantiallyelongated tri-phosphor light source having a substantially opaque regionextending over a portion of the exterior circumferential surface thereoffrom about one end portion of said light source to about the other endportion thereof, and a substantially transparent region extending overthe remaining portion of the exterior circumferential surface of saidlight source; heating means entrained substantially about the opaqueregion of the exterior circumferential surface of the light source andarranged to supply energy to the ligh source, said heating means beingan arcuate member arranged to mount slidably on said light source insubstantial contact with the opaque region of the exteriorcircumferential surface thereof, said arcuate member Extending in alongitudinal direction from about the region of one end portion of saidlight source to about the region of the other end portion thereof andhaving a slot therein extending in a longitudinal direction from one endportion of said light source to the other end portion thereof permittinglight rays transmitted through the transparent region of said lightsource to pass therethrough; means for cooling the light source, saidcooling means being spaced from the light source; and means forregulating said cooling means and said heating means to maintain thelight source substantially at about a predetermined temperature.
 9. Aprinting machine as recited as claim 8, wherein said arcuate memberextends circumferentially preferably, about 270*.
 10. A printing machineas recited in claim 8, wherein said cooling means includes blower meansadapted to create a flow of air upon the light source.
 11. A printingmachine as recited in claim 8, wherein said regulating means includes: athermally responsive member contacting the exterior peripheral surfaceof the light source for detecting the temperature thereof; and circuitmeans operatively associated with said thermally responsive member forenergizing said heating means when said thermally responsive memberindicates that the temperature of the light source is beneath apredetermined value, said circuit means being adapted to de-energizesaid heating means when said thermally responsive member indicates thatthe temperature of the light source exceeds the predetermined value. 12.A printing machine as recited in claim 11, wherein the predeterminedvalue of the temperature of the light source ranges from about 90* F toabout 115* F, and preferably is about 100* F.
 13. A printing machine asrecited in claim 8, wherein said regulating means includes a thermallyresponsive member contacting the exterior peripheral surface of thelight source for detecting the temperature thereof, said thermallyresponsive member energizing said heating meanS when the temperature ofthe light source is beneath a predetermined lower value of de-energizingsaid heating means when the temperature of the light source is above apredetermined upper valve.
 14. A printing machine as recited in claim13, wherein the lower value of the temperature of the light sourcepreferably is about 100* F and the upper valve of the temperature of thelight source preferably is about 110* F.